As a conventional switching valve for flow type analysis of this type, there are a six-way two-position switching valve, a multiposition valve which selects one flow path from among a plurality of connection ports, the valve discussed in Patent Document 1, and the like. These valves are used in order to switch between an analysis column and a drain flow path that are installed on the downstream side and to switch the flow path for selecting from among a plurality of columns.
In addition, as a conventional liquid feed mechanism for flow type analysis of this type, there is a plunger reciprocating type liquid feed pump that feeds a carrier liquid (eluent) by reciprocating operations of the plunger. In a plunger reciprocating type liquid feed pump, the plunger is reciprocated inside a pump head by using a mechanism for converting the rotary motion of a drive motor into linear motion. Due to the action of a check valve and a flow path switching valve respectively provided on the side of a liquid inlet and a liquid outlet of the pump head, the carrier liquid is drawn into the pump head, and then the liquid is discharged toward a sample injection device and a detection device.
As the plunger reciprocating type liquid feed pump, there are a single plunger pump provided with a pair of plungers and a pump head and a double plunger pump including two pairs of plungers and a pump head arranged in parallel or in series. In a plunger reciprocating type liquid feed pump, the plunger is reciprocated to repeat discharge motion and suction motion to perform feeding of liquid. The motion cycle of the liquid feed pump used in a normal flow type analysis apparatus is not synchronized with the analysis time and the analysis cycle, i.e., it is independently set irrespectively of the analysis time and the analysis cycle.
In performing feeding of liquid by using the above-described pumps, it is necessary to release air from an inside of the pump as a preparation for the liquid feeding. Typically, a drain valve included in a liquid feed apparatus is opened to secure a drain flow path for releasing air before performing air bleeding by feeding a large amount of carrier liquid (e.g., the carrier liquid can be fed in the flow rate of 2 mL/min or the like). In performing this air bleeding, it is necessary that the volume corresponding to one stroke of the plunger is greater than the volume of a liquid contact portion of the check valve. The volume corresponding to one stroke of the plunger differs according to the configuration of the entire flow type analysis apparatus and can be empirically set. For example, if the volume is set in consideration of the dimension of the flow type analysis apparatus, then if the volume of the liquid contact portion of the check valve is set to be in the range of 40 to 100 μL, the volume corresponding to one stroke of the single plunger pump becomes approximately 230 μL.